//! 集群故障检测与自动恢复模块
//! 
//! 实现Redis集群的故障检测和自动故障恢复功能：
//! - 节点故障检测
//! - 自动主从切换
//! - 故障恢复选举
//! - 集群状态恢复

use crate::cluster::traits::{
    FailureDetector, FailoverManager as FailoverManagerTrait, FailureStats, FailoverStatus as FailoverStatusTrait
};
use crate::cluster::{ClusterResult, NodeRole};
use async_trait::async_trait;
use serde::{Deserialize, Serialize};
use std::collections::{HashMap, HashSet};
use std::sync::Arc;
use std::time::{Duration, Instant};
use tokio::sync::{mpsc, RwLock};
use tokio::time::interval;
use tracing::{debug/*, error*/, info, warn};

/// 故障转移状态
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum FailoverState {
    /// 正常状态
    Normal,
    /// 主节点故障
    MasterFailed,
    /// 选举进行中
    ElectionInProgress { 
        epoch: u64,
        candidate: String,
        phase: ElectionPhase,
    },
    /// 故障状态
    Failed,
}

/// 选举阶段
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum ElectionPhase {
    /// 投票阶段
    Voting,
    /// 等待确认
    WaitingConfirmation,
    /// 选举完成
    Completed,
}

/// 故障转移配置
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct FailoverConfig {
    /// 选举超时时间
    pub election_timeout: Duration,
    /// 投票超时时间
    pub vote_timeout: Duration,
    /// 最大选举尝试次数
    pub max_election_attempts: u32,
    /// 心跳间隔
    pub heartbeat_interval: Duration,
    /// 故障检测间隔
    pub failure_detection_interval: Duration,
    /// 选举所需最小从节点数
    pub min_slaves_for_election: usize,
    /// 节点超时时间
    pub node_timeout: Duration,
}

impl Default for FailoverConfig {
    fn default() -> Self {
        Self {
            election_timeout: Duration::from_secs(5),
            vote_timeout: Duration::from_secs(3),
            max_election_attempts: 3,
            heartbeat_interval: Duration::from_secs(1),
            failure_detection_interval: Duration::from_secs(2),
            min_slaves_for_election: 1,
            node_timeout: Duration::from_secs(15),
        }
    }
}

/// 投票请求
#[derive(Debug, Clone)]
pub struct VoteRequest {
    /// 候选人节点ID
    pub candidate_id: String,
    /// 失败的主节点ID
    pub failed_master_id: String,
    /// 选举纪元
    pub election_epoch: u64,
    /// 需要的票数
    pub required_votes: usize,
    /// 已获得的投票
    pub votes: HashSet<String>,
}

impl VoteRequest {
    pub fn new(
        candidate_id: String,
        failed_master_id: String,
        election_epoch: u64,
        required_votes: usize,
    ) -> Self {
        Self {
            candidate_id,
            failed_master_id,
            election_epoch,
            required_votes,
            votes: HashSet::new(),
        }
    }
    
    /// 检查是否获得了多数票
    pub fn has_majority(&self) -> bool {
        self.votes.len() >= self.required_votes.div_ceil(2)
    }
}

/// 故障转移事件
#[derive(Debug, Clone)]
pub enum FailoverEvent {
    /// 主节点故障
    MasterFailed { master_id: String },
    /// 开始选举
    ElectionStarted { candidate_id: String, epoch: u64 },
    /// 选举完成
    ElectionCompleted { new_master_id: String, epoch: u64 },
    /// 选举失败
    ElectionFailed { candidate_id: String, reason: String },
    /// 故障恢复
    FailoverCompleted { old_master_id: String, new_master_id: String },
}

/// 从节点信息
#[derive(Debug, Clone)]
pub struct SlaveInfo {
    pub node_id: String,
    pub state: FailoverState,
    pub last_heartbeat: Option<Instant>,
}

/// 故障转移状态信息
#[derive(Debug, Clone)]
pub struct FailoverStatus {
    pub node_id: String,
    pub role: NodeRole,
    pub state: FailoverState,
    pub master_id: Option<String>,
    pub slaves: HashMap<String, SlaveInfo>,
    pub current_epoch: u64,
}

impl From<FailoverStatus> for FailoverStatusTrait {
    fn from(status: FailoverStatus) -> Self {
        FailoverStatusTrait {
            is_in_failover: !matches!(status.state, FailoverState::Normal),
            current_master: status.master_id,
            election_in_progress: matches!(status.state, FailoverState::ElectionInProgress { .. }),
            votes_received: 0, // TODO: 从选举状态中获取
            votes_needed: 0,   // TODO: 从选举状态中获取
        }
    }
}

/// 故障检测器
pub struct ClusterFailureDetector {
    /// 节点ID
    node_id: String,
    /// 可疑节点列表
    suspected_nodes: Arc<RwLock<HashMap<String, Vec<String>>>>, // node_id -> reporters
    /// 故障检测配置
    config: FailoverConfig,
    /// 运行状态
    is_running: Arc<RwLock<bool>>,
    /// 统计信息
    stats: Arc<RwLock<ClusterFailureStats>>,
}

/// 故障检测统计信息
#[derive(Debug, Clone, Default)]
pub struct ClusterFailureStats {
    pub suspected_nodes: usize,
    pub failed_nodes: usize,
    pub detection_cycles: u64,
    pub false_positives: u64,
}

impl From<ClusterFailureStats> for FailureStats {
    fn from(stats: ClusterFailureStats) -> Self {
        FailureStats {
            suspected_nodes: stats.suspected_nodes,
            failed_nodes: stats.failed_nodes,
            detection_cycles: stats.detection_cycles,
            false_positives: stats.false_positives,
        }
    }
}

impl ClusterFailureDetector {
    /// 创建新的故障检测器
    pub fn new(node_id: String, config: Option<FailoverConfig>) -> Self {
        Self {
            node_id,
            suspected_nodes: Arc::new(RwLock::new(HashMap::new())),
            config: config.unwrap_or_default(),
            is_running: Arc::new(RwLock::new(false)),
            stats: Arc::new(RwLock::new(ClusterFailureStats::default())),
        }
    }
}

#[async_trait]
impl FailureDetector for ClusterFailureDetector {
    async fn start(&mut self) -> ClusterResult<()> {
        let mut running = self.is_running.write().await;
        if *running {
            return Ok(());
        }
        *running = true;
        
        info!("启动故障检测器: {}", self.node_id);
        
        // 启动故障检测任务
        let _suspected_nodes = self.suspected_nodes.clone();
        let stats = self.stats.clone();
        let is_running_clone = self.is_running.clone();
        let detection_interval = self.config.failure_detection_interval;
        
        tokio::spawn(async move {
            let mut interval = interval(detection_interval);
            
            while *is_running_clone.read().await {
                interval.tick().await;
                
                // 更新检测周期统计
                {
                    let mut stats = stats.write().await;
                    stats.detection_cycles += 1;
                }
                
                // TODO: 实现实际的故障检测逻辑
                debug!("执行故障检测周期");
            }
        });
        
        Ok(())
    }
    
    async fn stop(&mut self) -> ClusterResult<()> {
        let mut running = self.is_running.write().await;
        *running = false;
        info!("故障检测器已停止: {}", self.node_id);
        Ok(())
    }
    
    async fn report_suspected_node(&mut self, node_id: String, reporter: String) {
        let mut suspected = self.suspected_nodes.write().await;
        let reporters = suspected.entry(node_id.clone()).or_insert_with(Vec::new);
        
        if !reporters.contains(&reporter) {
            reporters.push(reporter.clone());
            info!("节点 {} 被 {} 报告为可疑", node_id, reporter);
            
            // 更新统计信息
            let mut stats = self.stats.write().await;
            stats.suspected_nodes = suspected.len();
        }
    }
    
    async fn get_suspected_nodes(&self) -> Vec<String> {
        let suspected = self.suspected_nodes.read().await;
        suspected.keys().cloned().collect()
    }
    
    async fn clear_suspected_node(&mut self, node_id: &str) {
        let mut suspected = self.suspected_nodes.write().await;
        if suspected.remove(node_id).is_some() {
            info!("清除节点 {} 的可疑状态", node_id);
            
            // 更新统计信息
            let mut stats = self.stats.write().await;
            stats.suspected_nodes = suspected.len();
            stats.false_positives += 1;
        }
    }
    
    async fn is_node_suspected(&self, node_id: &str) -> bool {
        let suspected = self.suspected_nodes.read().await;
        suspected.contains_key(node_id)
    }
    
    async fn get_failure_stats(&self) -> FailureStats {
        let stats = self.stats.read().await;
        stats.clone().into()
    }
}

/// 故障转移管理器
pub struct ClusterFailoverManager {
    /// 节点ID
    node_id: String,
    /// 节点角色
    role: NodeRole,
    /// 故障转移状态
    state: Arc<RwLock<FailoverState>>,
    /// 从节点信息
    slaves: Arc<RwLock<HashMap<String, SlaveInfo>>>,
    /// 主节点ID（如果是从节点）
    master_id: Arc<RwLock<Option<String>>>,
    /// 当前选举纪元
    current_epoch: Arc<RwLock<u64>>,
    /// 配置
    config: FailoverConfig,
    /// 事件发送器
    event_sender: mpsc::UnboundedSender<FailoverEvent>,
    /// 事件接收器
    event_receiver: Arc<RwLock<Option<mpsc::UnboundedReceiver<FailoverEvent>>>>,
    /// 运行状态
    is_running: Arc<RwLock<bool>>,
}

impl ClusterFailoverManager {
    /// 创建新的故障转移管理器
    pub fn new(
        node_id: String,
        role: NodeRole,
        config: Option<FailoverConfig>,
    ) -> Self {
        let (event_sender, event_receiver) = mpsc::unbounded_channel();
        
        Self {
            node_id,
            role,
            state: Arc::new(RwLock::new(FailoverState::Normal)),
            slaves: Arc::new(RwLock::new(HashMap::new())),
            master_id: Arc::new(RwLock::new(None)),
            current_epoch: Arc::new(RwLock::new(0)),
            config: config.unwrap_or_default(),
            event_sender,
            event_receiver: Arc::new(RwLock::new(Some(event_receiver))),
            is_running: Arc::new(RwLock::new(false)),
        }
    }
    
    /// 获取事件接收器
    pub async fn take_event_receiver(&self) -> Option<mpsc::UnboundedReceiver<FailoverEvent>> {
        self.event_receiver.write().await.take()
    }
}

#[async_trait]
impl FailoverManagerTrait for ClusterFailoverManager {
    async fn start(&mut self) -> ClusterResult<()> {
        let mut running = self.is_running.write().await;
        if *running {
            return Ok(());
        }
        *running = true;
        
        info!("启动故障恢复管理器: {}", self.node_id);
        
        // 启动心跳任务
        let slaves = self.slaves.clone();
        let is_running_clone = self.is_running.clone();
        let heartbeat_interval = self.config.heartbeat_interval;
        
        tokio::spawn(async move {
            let mut interval = interval(heartbeat_interval);
            
            while *is_running_clone.read().await {
                interval.tick().await;
                
                // 检查从节点心跳
                let mut slaves = slaves.write().await;
                let now = Instant::now();
                
                for (node_id, slave_info) in slaves.iter_mut() {
                    if let Some(last_heartbeat) = slave_info.last_heartbeat {
                        if now.duration_since(last_heartbeat) > Duration::from_secs(10) {
                            warn!("从节点 {} 心跳超时", node_id);
                            slave_info.state = FailoverState::Failed;
                        }
                    }
                }
            }
        });
        
        Ok(())
    }
    
    async fn stop(&mut self) -> ClusterResult<()> {
        let mut running = self.is_running.write().await;
        *running = false;
        info!("故障恢复管理器已停止: {}", self.node_id);
        Ok(())
    }
    
    async fn start_election(&mut self) -> ClusterResult<()> {
        let mut epoch = self.current_epoch.write().await;
        *epoch += 1;
        let election_epoch = *epoch;
        
        let mut state = self.state.write().await;
        *state = FailoverState::ElectionInProgress {
            epoch: election_epoch,
            candidate: self.node_id.clone(),
            phase: ElectionPhase::Voting,
        };
        
        info!("开始选举: 候选人 {}, 纪元 {}", self.node_id, election_epoch);
        
        // 发送选举开始事件
        let _ = self.event_sender.send(FailoverEvent::ElectionStarted {
            candidate_id: self.node_id.clone(),
            epoch: election_epoch,
        });
        
        // TODO: 实现实际的选举逻辑
        // 1. 向其他节点发送投票请求
        // 2. 收集投票
        // 3. 检查是否获得多数票
        
        Ok(())
    }
    
    async fn vote_for_candidate(&mut self, candidate_id: &str) -> ClusterResult<()> {
        info!("投票给候选人: {}", candidate_id);
        
        // TODO: 实现投票逻辑
        // 1. 验证候选人资格
        // 2. 检查是否已经投票
        // 3. 发送投票响应
        
        Ok(())
    }
    
    async fn become_master(&mut self) -> ClusterResult<()> {
        info!("节点 {} 成为新的主节点", self.node_id);
        
        // 更新角色和状态
        self.role = NodeRole::Master;
        *self.state.write().await = FailoverState::Normal;
        *self.master_id.write().await = None;
        
        // 发送故障恢复完成事件
        let _ = self.event_sender.send(FailoverEvent::FailoverCompleted {
            old_master_id: "unknown".to_string(), // TODO: 记录实际的旧主节点ID
            new_master_id: self.node_id.clone(),
        });
        
        Ok(())
    }
    
    async fn get_failover_status(&self) -> FailoverStatusTrait {
        let state = self.state.read().await;
        let master_id = self.master_id.read().await;
        let slaves = self.slaves.read().await;
        let current_epoch = *self.current_epoch.read().await;
        
        let failover_status = FailoverStatus {
            node_id: self.node_id.clone(),
            role: self.role.clone(),
            state: state.clone(),
            master_id: master_id.clone(),
            slaves: slaves.clone(),
            current_epoch,
        };
        
        failover_status.into()
    }
}

